A Biotechnological Strategy to Improve Indigenous Potato Cultivars of Bangladesh with Enhanced Starch Content

Abstract

Present study was under taken with a view to improve the yield potential of indigenous (local) potato varieties (IPVs). Six IPVs viz., Lap Shill, Patna, Shill Billet, Lap Parke, Sade Gutty and Challis were selected as experimental materials. This IPV s is popular among the potato growers of the Northern part of Bangladesh because of their high value due to high culinary quality and storability. However, tuber yield of these IPVs substantially decreased. They are cleverly infected with different viral diseases. In the present study three in vitro techniques viz., i) heat treatment followed by merriest culture for the development of virus free planting materials; ii) induction of micro tuber for rapid production of virus free planting materials and iii) induction and evaluation of soma clonally variation were employed for the varietal improvement of the selected IPVs. For the development of virus free planting materials, shoot tip explants of five weeks old tuber grown shoots of six IPV s were cultured on to MS0-agar medium and incubated in an incubator in dark at three different temperature regimes (37°C, 42°C and 47°C) and incubated for 10, 5 and 3 days, respectively. The shoot tip cultures were then transferred in a plant growth chamber and incubated for three weeks at 22°C in 16h/8h light/dark condition. The merriest were isolated from the shoot tips of in vitro grown plantlets. Individual merriest derived plantlets were carefully multiplied by node cutting and analyzed for potato virus X(PVX), Y(PVY) and potato leaf roll virus (PLRV) through ELISA. Thermal shock of in vitro grown plantlets at 47°C followed by merriest culture was found to be the best technique for virus elimination among tested IPV s. It was found that virus eradication from the indigenous varieties was very difficult. Shoot multiplication into MS semisolid basal medium supplemented with different cytokine’s, axons and GA3 either singly or in combination resulted that media formulation with 0.5 mg/I BAP + 0.5 mg/I GA3 found to be the best media formulation for merriest culture establishment and subsequent shoot proliferation. Among the carbon sources sucrose was found to be the best and 3% sucrose was better than 6% sucrose for merriest derived shoot proliferation. The tuber yield/plant of in vitro produced plantlets in the field was much better than the tuber grown plants. Furth encore, in vitro produced plantlets of all the indigenous varieties having nominal plant height produced more but smaller tubers/plant than the tuber derived plants. The aim of next part of the present investigation was to establish a standardized protocol for large scale in vitro propagation of virus free planting materials through in vitro tube relation for four IPV s (Lap Shill, Patna, Shill Balata and Lap Parke). Micro tubers were induced in vitro to merriest derived shoots by manipulating the concentration of BA, KIN and sucrose in MS medium. Between two cytokine’s, KIN showed better performance than BA in micro tuber induction. Among the six concentrations (2-12 mg/I) of KIN, 10 mg/I KIN was the most effective and more preferred concentration for micro tuber induction. In continuous dark it was observed that increase the level of KIN also increased the percentage of tube relation and number and weight of micro tuber/shoot. By increasing the concentration of sucrose increased the frequency of in vitro tube relation. The media containing 60 g/1 was found to be the best among seven concentrations (20-80 g/1) of sucrose tested followed by 70 g/1 sucrose for micro tuber induction for all four IPVs. Assessment of the effect of photoperiods on micro tuber induction showed that longer photoperiod condition was better for in vitro tube relation at all levels of KIN for all four IPV s. Short day photoperiod gave a response similar to continuous dark. The 24 h photoperiods produced significantly more micro tubers than 0 (continuous dark) and 8 h photoperiods at all levels of KIN. The micro tubers induced to develop in 8 mg/I KIN supplied medium had shorter dormant period (time taken from harvesting to sprouting). Field evaluation results indicated that among four IPVs higher tuber weight was found in IPV Patna. The third part of this study was carried with a view to optimize culture media foundation for callus induction and subsequent plant regeneration in four IPV s (Lap Shill, Patna, Shill Billet and Lap Parke). The callus derived plantlets of four IPVs were transplanted on to field and possible occurrence of some clonally variation was evaluated. Two types of explants taken from in vitro shoots of four IPVs were cultured on to MS medium supplemented with various axons and cytokine’s. It was observed that 2,4-D was the best axing when used singly for callus induction in potato and 2.5 mg/I was found to be the most effective in callus induction. Between two types of explants, intermodal explants were found more responsive than leaf explants for callus formation. The combinations of BA+NAA and KIN+NAA combination was found more effective for shoot regeneration for intermodal and leaf explants derived calla. BA+NAA combination was found to be more effective than KIN+NAA for maximum shoot induction from leaf explants derived calla. Among various treatments, the media fortified with 3.0 mg/I BA+0.l mg/I NAA and 3.0 mg/I BA+ 1.0 mg/I NAA were found to be the best formulations. The highest 50% calla derived from intermodal explants induced to develop multiple shoots regeneration in medium having 4.0 mg/I KIN+ 1.0 mg/I NAA. Plants regenerated through callus culture displayed pronounced some clonally variations for plant height, number of leaves/plant, number of tubers/plant, tuber weight/plant and starch content in tuber. Some of the some clones showed promisingly higher amount of tuber yield per plant with enhanced starch content in the tuber. This variation may be useful for varietal improvement of this IPV s, but further study is needed for this.